1. Field of the Invention
The present invention relates to a method of and an apparatus for manufacturing a web composed of a plurality of filaments aligned in a transverse direction.
The web obtained according to the present invention is excellent in mechanical strength and dimensional stability, and can be used as a raw material web for nonwoven fabric needed to have strength in one direction and for cross laminated nonwoven fabric.
2. Description of the Related Art
As a method of manufacturing a nonwoven fabric, there have been a spun-bonding method, a melt-blowing method and a flush-spun method, all these methods being conducted during spinning yarns therefore, and the obtained fabric will be hereinafter referred to as a spunbonded nonwoven fabric in broad sense. Since nonwoven fabrics manufactured by the above-mentioned methods are economical and mass-producible, these methods are the mainstream of nonwoven fabrics.
These conventional spunbonded nonwoven fabrics in broad sense are randomly nonwoven fabrics in which filaments are randomly aligned, and therefore many of them are of small mechanical strength and have no dimensional stability. The present inventors have invented a stretching method of nonwoven fabrics and a method of manufacturing nonwoven fabric in which nonwoven fabrics manufactured by the stretching method are laminated in a manner such that respective fabrics are aligned to be perpendicularly to one another in order to eliminate the drawbacks the conventional nonwoven fabric (see Japanese Patent Publication No. 36948/91).
Also, the present inventors have conducted research and development in a web having filaments aligned in a transverse direction and capable of being used as raw material web for the above-mentioned cross laminated nonwoven fabric (Japanese Patent Nos. 1992584 (Japanese Laid-open Patent Publication No. 242960/90) and 2612203 (Japanese Laid-open Patent Publication No. 269859/90)). The web having filaments aligned in the transverse direction be hereinafter referred to as a transversely aligned web.
Due to the recent advance in the nonwoven fabric industry, it has been further desired that the cross laminated nonwoven fabric be more improved in its quality and productivity.
Nevertheless, although the manufacturing method of the transversely aligned web by the spraying method as disclosed in Japanese Patent Publication No. 36948/91 and Japanese Patent No. 1992584 can be an effective means for aligning filaments in the transverse direction, due to a large amount of extrusion as per one nozzle, and a good alignability of filaments in the transverse direction, a single spinning gun can be provided with only one nozzle. Thus, even if productivity as per one nozzle is large, many spinning guns are required in order to increase the amount of production. Also, the width of web obtained by this method must be limited to at most approximately 400 through 500 mm, and it is difficult to produce web having a larger width. Further, when it is tried to increase the alignability of filaments in the transverse direction, each of the side edge portions of the web (it is often referred to as a selvage) becomes large in thickness, and therefore the yield of web must be reduced and the uniformity of the basis weight of the web is liable to deteriorate.
On the other hand, in a means for realizing the transverse alignment of filaments by applying various contrivances to a conveyor as disclosed in Japanese Patent No. 2612203, a spinning means employed in the spun-bonding method in broad sense may be used while obtaining a good productivity. However, the alignability of filaments in a transverse direction is insufficient.
Generally, in order to obtain web in which filaments are sufficiently aligned in a transverse direction, it is not sufficient to align the filaments in the transverse direction in the spinning process. Also, the mechanical strength of filaments per se obtained in the spinning process is generally small. It is considered that the best method for increasing the alignability of filaments in the transverse direction and the mechanical strength of filaments per se is to stretch the web in the transverse direction. However, after the spinning process, generally the web cannot well be stretched in the transverse direction because the filaments are not well aligned transversely and are not sufficiently cooled, and it is difficult to stretch the web to high mechanical strength at a high magnification.